Three-dimensional (3D) organic-inorganic perovskites are promising thin film materials for optoelectronic devices due to their remarkable photophysical properties. For example, in solar cells, 3D perovskite materials have shown power conversion efficiencies exceeding 20%, with the prospect of further improvements towards the Shockley-Queisser limit for a single-junction solar cell. However, a lack of environmental stability (e.g., to moisture) and photostability under operating conditions are critical factors against the use of 3D perovskite materials in photovoltaics and other optoelectronic applications. In addition, anomalous hysteresis effects have greatly reduced reproducibility in these devices.
Layered two-dimensional (2D) perovskite films, such as Ruddlesden-Popper phase perovskites, have shown promising stability in optoelectronic applications. However, they have shown poor power conversion efficiencies of only 4.73%. This may be attributed to inhibition of out-of-plane charge transport by organic cations, which act like insulating spacing layers between the conducting inorganic components. Accordingly, the efficiencies of these layered 2D perovskite materials has limited their applicability in optoelectronic applications.